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Author Topic: ok, warranty is up, so now adding solar (for one of my roof top ac's)  (Read 287 times)

lmichel

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I want to run this:
https://www.dometic.com/en-us/us/products/climate/air-conditioners/air-conditioners-for-rvs/dometic-penguin-ii-_-20782#specifications

It's a roof-mount AC that draws about 1400W or 12amps@120v
And I *ONLY* want to run that.
In fact, my plan is to disconnect it from the existing service and run it (dedicated) to the array/battery bank.

I'm thinking I over-engineered this, but I've spec'd out 3 panels at 335W each.  9amps and VOC@40v  (I have the roof space)
Run all three in series to a bank of 4 L16s (Trojan L16RE-B 6v) connected in series.
From the batteries to a 24v inverter ..  4000w  (Magnum Energy MS4024)
Not sure about the charge controller, It's only going to need to handle about 10amps in at 120v max.  However, it should also have a heavy charge output to keep those 4 L16's topped off?

The weight/space isn't a problem.  It's all going into the garage of a 2016 Thor 37RB, which is spec'd to hold 2800lbs!

I'm not planning to touch the existing coach battery system.  It'll continue to do what it does.  The PV system is only for one of the 2 roof-tops when boondocking and I'm fine also using it when at a campground, even though I might have full hook ups. 

QUESTIONS:
1. Looks like I could run that AC unit 24hrs on a cloudy day with a full charge.  Do you agree?
2. What charge controller would you select?
3. I don't need a big 4000w inverter, but to go from 2kw to 4kw is only $100.  So why not do it??
4. All inverters seem to have a built in charger.  I doubt I'd ever use it?  Wasn't even planning to connect it to the shore circuit.
5. Is this system so huge that I should consider running both ACs?  I figured I should't anyway - for redundancy reasons..

I have an Onan 5500w, but it sucks!  Thor wont replace it and it has been in the shop 4 times.  They replaced the fuel pump, filter, controller board, ignition coil and plugs.  It runs for roughly 30 minutes, starts hunting and then shuts down.  It cranks but won't start for a couple hours and then the whole cycle starts over again.  Screw generators!  I've had it with them!
Oh and screw Thor too :)

Thanks!
Lance
« Last Edit: June 25, 2017, 07:55:10 AM by lmichel »

Alfa38User

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Good Luck!!! But, be aware that solar panels put out DC, the same as a battery and they cannot run an AC appliance alone such as an air conditioner. It will require an inverter drawing from the batteries and that 1400 watts (12Amps) AC suddenly becomes 116 amps @12V DC or about 58 amps at 24V plus the inefficiencies of the conversion AND the very large startup inrush currents. Won't take long to kill those batteries when full solar is not available.
Stu
Montréal, Canada 🍁
Snowbird, Naples Florida
Alfa Gold 38 (2000) 5ver (parked!)

"Of course I talk to myself, sometimes I need expert advise!!!"

lmichel

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That's why I spec'd a 4Kw inverter! 
The Locked Rotor draw for the compressor on that AC unit is 22amps@50ms  - a 4Kw inverter could continuously run at that draw.
But I was off by an order of magnitude.  I'm not going to get anywhere close to 24hrs with a full charge.  More like about 2.4hrs :(

Back to the drawing board..

glen54737

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You will want a charge controller to use the 40v from the solar panels to charge a 24v battery bank.
I don't think you will have the amp-hours to run for more than 4 hours depending on duty cycle of the ac.
I'd like to know how it works out.
2018 Thor Miramar 35.2
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AStravelers

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You probably already know what I am writing, but I just wanted to put some numbers to your project.

So you will have 740 AH (Amp Hours) of battery capacity, of which only about 200 AH (25% of capacity) is usable to provide long life for your batteries.  Trying to go to using 50% of capacity really reduces the life of very expensive batteries. 

You solar panels will provide a max of about 20 amps of 12V current per solar panel on a bright sunny day in the southern part of the USA in the summer.  This power is dependent on using a MPPT solar controller.  Total of around 60 amps charging to your battery pack. Less on a cloudy day.  How much power you get out of your panels on cloudy day depends on how thick the cloud cover is.  You will still get quite a bit of power on an overcast day. 

Bottom line is just how long you can run your AC will depend a lot on how much power is coming out of your solar panels to reduce the draw on the batteries. 

If you really intend to run an AC off of battery you would be much better off to use lithium batteries.  With 800 AH of lithium you will have about 600 AH of usable capacity (75% of the total).  With the expense of the Trojan batteries, you could be at 50-75% of the cost of lithium.

Here are some links to folks who are using lithium and some info about running AC on battery.

This one has a huge amount of info.  Be sure to scroll down a ways to find about 6 articles on Solar, batteries, air conditioners, etc.
http://www.technomadia.com/solar/

Here is another link to a 4 part series on lithium install and operation.
http://wheelingit.us/2016/02/24/the-big-beastly-solarbattery-upgrade-part-i-why/

Al & Sharon
2006 Winnebago Sightseer 29R
2009 Chevy Colorado 4X4

http://downtheroadaroundthebend.blogspot.com/

lmichel

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Interesting, I already follow Technomedia..   Great Youtube content :)

If I'm not mistaken, a LiON bank of 800AH will cost me north of $10,000
4 L16RE-b's will cost me about $1500.  At that rate, I could go ahead an abuse them with a 50% SOC cycle and plan to replace them early.  They will still beat the pants off the cost of the lithium bank.  No?

Thank for the second look at my calc's  I really do appreciate it!

Kevin Means

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A few years ago, Newmar offered an option on one of their high end coaches (the King Aire, I think) for an expanded battery-bank. I think there were 12 high capacity house-batteries in the basement, and they were capable of running at least one roof AC unit. I don't know if that option is available anymore, or not.

Powering a roof AC unit off an inverter and large battery-bank is doable, but it's never been very practical. They just consume too much power from even large RV battery-banks. Some RVers have used smaller 5000 or 6000 BTU room units with some success, but even those will tax an RV's battery-bank. I understand your frustration with the genset, but for powering AC units, it's a much more practical solution.

Kev 
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ or an Acura MDX
RVI Brake 2, Minder TM-66 TPMS, 970 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California

Gary RV_Wizard

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4 x L16's in series only provide 370 AH, though at 24v. When in series, the AH doesn't add - just the voltage. You don't have anywhere near enough battery bank to power a high demand device such as an a/c. Even for a few hours. Only about half the battery capacity is usable before it runs down so much that voltage drops a lot. The battery life is also adversely affected.

Don't know where you are shopping but there are standalone inverters (no charger) available. Here is one source:
http://invertersrus.com/product-category/power-inverters/pure-sine-wave/24v-psw/page/2/
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

lmichel

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Thanks Gary,
Yep, AHs don't multiply when in series.  But the available wattage does.  1 L16 (6v) could provide 2220 watts over a 20hr period.
Or, to put it another way, 111 crummy watts or 111/6=18.5amps steady for 20hrs.  After which, you would have one hurting battery.  Best to plan for half that, probably even less if you wanna be nice to the battery.

Put four together in series and now you can have about 9.25(amps)*6(volts)*4(batteries) = about 222 watts steady for that 20hrs.  The bank would be 50% depleted.  But I'm gonna push it.  I'm gonna make the bank give me 1400w (350w each), but for only 2.5hrs.  And better yet, I'm going to spread that 2.5hrs of run time across 5hrs. (50% duty cycle). 

Now, I'm also going to offset that usage by the 1000 watts of solar.  Figure another 5kWh thrown into the pool of available energy for the day.  That gives me another 5000/1400=3.5hrs..  or 7hrs at the 50% duty cycle. 

Add it all up, and I can run the unit 50% of the time for 12hrs.  And... at the end, I'll only be half depleted.  My 'State of Charge' will be 50%.  Not babying the bank, but certainly not crushing it either.  I figure it'll give me 1500 cycles treating it like that.  Heck, that's 4 years if I ran it everyday that way.  And that's very, very unlikely.

Invertersrus.com is exactly the hint I needed :)  Thank you!  Looks like COTEK has a 24v/4000W Inverter without a charger that would fit the bill, and at half the price of a Magnum Energy that include the charger.

Again, thanks for the help!  Much appreciated!

« Last Edit: June 25, 2017, 02:15:50 PM by lmichel »

AStravelers

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Interesting, I already follow Technomedia..   Great Youtube content :)

If I'm not mistaken, a LiON bank of 800AH will cost me north of $10,000
4 L16RE-b's will cost me about $1500.  At that rate, I could go ahead an abuse them with a 50% SOC cycle and plan to replace them early.  They will still beat the pants off the cost of the lithium bank.  No?

Thank for the second look at my calc's  I really do appreciate it!
Here is a 800AH battery kit for just under $7000: http://www.lithiumrvbattery.com/Lithium_RV_Battery/GBS_200AH_Cells.html  Not cheap but is less than $10K.   

However 
Quote
4 L16RE-b's will cost me about $1500.  At that rate, I could go ahead an abuse them with a 50% SOC cycle and plan to replace them early.  They will still beat the pants off the cost of the lithium bank.  No?
 
Ah, NO the L16RE's will not beat the pants off the lithium.  Not if you have any thoughts of running a really high load like an air conditioner.   

Two things:
--  The lithium batteries maintain a pretty much constant voltage, under heavy load, of about 13.3-13.4 V from 100% to 30% SOC.  The lead acid batteries will be dropping down to 12.2 or even close to 12.0 volts under the heavy load.
--  The 800AH lithium will take a 200AH charge rate for the full 2-3 hours it take to put back 400AH or 600AH needed.  The lead acid will start accepting the 200AH but then start tapering off quickly.  The last 40% to 20% of charging will take quite a few hours to push back in the battery.  You are unlikely to get the lead acid above 90% charged, possibly only 85% charged in the amount of time you have solar available. 

There is not question in my mind that anyone trying to run a really heavy load for a long period, that the a/c requires, lithium is the only way to go.   

You really must keep in mind the recharging ability and not just the discharging.  Taking 400AH out of your 800AH battery pack of lead acid and then just putting back in 250-300AH means you are starting off the next day at a deficit. The next day you don't have 400AH available any more.  The third day even less. 

The lead acid will work great if you will only take 200-300AH out but not if you plan on taking 400AH of your 800AH total. 

Another thought.  I have not attempted to do the detailed math on this.  But you probably want to have 1200-1600 watts of solar panels to be able to get enough AH's back in either the lithium or lead acid batteries, if you plan on taking out 400-600AH's. 
« Last Edit: June 30, 2017, 10:02:22 AM by AStravelers »
Al & Sharon
2006 Winnebago Sightseer 29R
2009 Chevy Colorado 4X4

http://downtheroadaroundthebend.blogspot.com/

Arch Hoagland

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Re: ok, warranty is up, so now adding solar (for one of my roof top ac's)
« Reply #10 on: June 30, 2017, 10:22:55 AM »
Interesting thread as I've been contemplating doing the exact same thing at my house. We use one room air conditioner almost exclusively to cool our den and kitchen where we spend most of our time.  105 degrees is normal for three months so our power bill is a bit high then.

My plan was to install several solar panels on the roof of a Tikihut hut we have in the back yard put a rack of batteries next to the window air conditioner along with the inverter equipment. I would wire the A/C directly to it.

My plan is to initially use several cheap 12 volt cars batteries just to see how long I can run, or indeed, if I can run at all.  Then I will go from there.

So I'll be watching this thread with great interest and to gain some knowledge from those of you who have done a similar thing.
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